This invention relates to an improved process for converting coal or similar solid carbonaceous materials. More particularly, this invention relates to an improved process for liquefying coal and similar carbonaceous substances.
As is well known, coal has long been used as a fuel in many areas. For several reasons, such as handling problems, waste disposal problems, pollution problems and the like, coal has not been a particularly desirable fuel from the ultimate consumers point of view. Moreover, coal cannot be used directly in areas where a liquid or gaseous fuel is required. As a result, oil and gas have enjoyed a dominant position, from the standpoint of fuel sources throughout the world.
As is also well known, proven petroleum and gas reserves are shrinking throughout the world and the need for alternate sources of energy is becoming more and more apparent. One such alternate source is, of course, coal since coal is an abundant fossil fuel in many countries throughout the world. Before coal will be widely accepted as a fuel, however, it is believed necessary to convert the same to a form which will not suffer from the several disadvantages alluded to previously and which will permit use in those areas where liquid or gaseous fuels are normally required.
To this end, several processes wherein coal is either liquefied and/or gasified have been proposed heretofore. Of these, the processes wherein coal is liquefied appear to be more desirable since a broader range of products is produced and these products are more readily transported and stored.
Of these several liquefaction processes which have been heretofore proposed, those processes wherein coal is liquefied in the presence of a solvent or diluent, particularly a hydrogen-donor solvent or diluent, and a hydrogen-containing gas appear to offer the greater advantages. In these processes, liquefaction is accomplished at elevated temperatures and pressures and hydrocarbon gases are invariably produced as by-products. For the most part, however, these processes result in high relative yields of higher boiling point liquids; i.e., products boiling in the fuel oil and vacuum gas oil ranges. The bulk of the products obtained from these processes, then, are at best substitutes for coal in applications where coal could be used directly. Moreover, and while some lighter products are produced there has, heretofore, been little control over the product distribution or the total amount of liquids actually produced. The need, therefore, for a liquefaction process which will increase the yield of liquid products and provide better control over the relative distribution of motor gasoline, jet fuel and heavier oils is believed to be readily apparent.